Place a medium ovenproof skillet in the center of the oven and preheat oven to 450oF (225oC). Let skillet heat for 10 minutes.
In a large bowl, beat the eggs until thick, about 2 minutes.
Once fluffy gradually stream in milk and 2 tablespoons of butter.
Add flour, cornstarch, salt, and pepper and whisk just to combine.
Carefully remove skillet from the oven and swirl remaining 1 tablespoon of butter in skillet to coat. Immediately pour batter into skillet (butter will brown quickly, so have batter at the ready to prevent burning).
Bake pancake until puffed and brown around edges, 15-20 minutes. It will begin to deflate as soon as it comes out.
Top with avocado, smoked salmon, dill and crème fraîche.